Where to Connect C Wire on the furnace? (Find Out!)
Are you trying to set up your furnace but have no idea where to connect the c wire? The wiring of a furnace can be confusing. This is especially true of you who do not usually work with wires. There are several options on where to connect the C-Wire. Here is one of them:
You first need to remove your thermostat panel from the wall. Then, look at the cabling and locate a terminal that is labeled “C”. That terminal is where you should connect your C-Wire.
You may not find a terminal that is labeled “C”. But this does not mean that your C-Wire cannot be connected. I will discuss alternative methods to connect your C-Wire to your furnace.
What is a C-wire?
A common wire (C-wire) supplies continuous power from the low voltage heating system to your thermostat. Many newer heating/cooling systems on the market today are manufactured with C-wires. This makes them compatible with many smart thermostat installations. If there is no low voltage heating/cooling system then, there will not be a C-wire. But there are a few options discussed below for those faced with such a scenario.
How to know if I have a C-wire?
There are two easy ways to know or find out whether you have C-wiring in your thermostat. These methods include checking your furnace or the circuit board of your furnace.
Check the back of your furnace
Before removing the backplate of the thermostat, always make sure to switch off the power supply to prevent electrocution. Once the backplate is removed and the wires are exposed, you will see many wire colors. These colored wires have terminals marked with letters such as G, W, C, R, Rc, O/B, and Y.
The easiest way to know if your wiring already has a common wire is to examine the backside of your thermostat. To do this examination, you may remove the faceplate and take the thermostat out of the wall. You will see wires coming into different terminals of your thermostat marked R, W, Y, G, Rc, C, and O/B. The terminal marked “C’ is what you are looking for. But, in some circumstances, there may be no C-terminal, especially in older models. Many older models may have C-terminals that are just unconnected so search for wires that may be concealed behind your thermostat. Then connect it once you have verified that it is indeed a C-terminal. This verification is done by examining your thermostat’s circuit board.
Examine the circuit board on your furnace
Like the thermostat, the furnace or heating system has similar alphabetical markings. Which include G, W, C, R, Rc, O/B, and Y. There are two wires of varying colors that are ‘tapped” from the C-wire. There is one that connects the C-wire to the thermostat and another wire to the condenser unit. If you are done, find any C-wires connecting to your furnace. However, there are options available to you, such as purchasing and adding a C-wire adapter to your furnace.
What do I do if I do not have a C-wire?
Add a C-wire adapter to your Furnace
A common wire adapter is a miniature electronic device, connected in place of a C-wire. It connects the thermostat and furnace. Hence enabling the furnace to provide the required power to the thermostat. This device is only relevant if you have no C-wiring. So you should make sure to thoroughly check for it before attempting to get an adapter.
Frequently Asked Questions
What does the C-wire connect?
A common wire’s main purpose is to connect your low voltage heating system/furnace and thermostat. So that there is a continuous supply of power(24V) flowing between the two. If you do not have C-wiring then you should get a C-Wire adapter. It will replace the missing C-wire. Enabling power to be supplied between the thermostat and furnace.
How can I tell if my C-wire has power?
One way to test if there is power is by removing the batteries from your thermostat. If you remove the batteries and the thermostat stays on then you know that it is working. This is because it will no longer be running on battery power but C-Wire power. I recommend that you keep your batteries in case of a power outage.